Am I right in saying that a deadlock is supposed to happen in the following case:
Object P calls a synch method of object A,
that calls a synch method of object B,
that calls a synch method of object A.
Sorry if it looks stupid of me, most probably it is. But that's why I'm asking. Thanks!
No. It is same thread, synch methods are reenterable.
If you take definition from wikipedia: "A deadlock is a situation wherein two or more competing actions are each waiting for the other to finish". You have only one action (thread) .
No, the thread will already hold the lock on A, so it won't deadlock. A thread can never contend for a lock with itself.
By the information you give - no, a deadlock can't occur:
First, you don't mention multiple threads. A single thread can't cause a deadlock. But let's assume you have multiple threads.
So, if any other object, from different thread invokes some of these methods in reverse order, then a deadlock can occur.
The explanation of the situation is as follows: Thread-1 obtains the lock required to enter methodA, and then tries to enter methodB. If at the same moment another thread - Thread-2 invokes methodB and obtains the lock for it, then tries to enter methodA, but Thread-1 already has the lock, so Thread-2 waits. However, Thread-1 can't enter methodB because Thread-2 has the lock. And they wait forever (deadlock).